That may work for model s market... But even they came up with model cheap, this will be all kinds of nightmare from smart ppl "returning" all sorts of junk batteries.
If all batteries are built and sold by Tesla, it would be easy to put battery health monitoring in there to test them before swapping them out. The cars are already all online and pinging home their battery level (see the stories about Tesla contacting owners who left their car in a garage and their battery is about to be irrecoverably discharged)
